Tag Archives: timekeeping

It’s 2 metals in 1!

This next part is crazy. I don’t know how Harrison dreamed up this idea. I don’t know how it’s even possible. Maybe a reader with experience in welding can help me out.*

Because metal springs are susceptible to temperature changes, which make them less reliable and accurate, Harrison invented the bimetallic strip. It is 2 metals, like steel and brass, welded together.

Did you get that? It’s possible to weld, or fuse, or something, steel and brass now. The watch’s mainspring needs always to be springy. When it’s cold, the spring becomes too stiff. When it’s hot, the spring becomes too loose. Harrison fused two metals together—steel and brass—in a spring. If the steel were too tight, the brass would keep it loose. If the brass were too loose, the steel would tighten it up. This way the spring would keep the same springiness no matter the temperature.

* This weekend I had the pleasure of consulting 2 engineers, my sister’s boyfriend Dave and my nephew Andrew. They tell me with enough heat, two different metals can be fused together. The two metals would be hammered together many times under heat until they were one. Andrew added that it’s only air molecules that keep metals from fusing together in the first place.





Back to the beginning of The Western Civ User’s Guide to Time & Space

Hot- and cold-running time

After breaking his heart trying to perfect a clock to keep accurate time on the high seas, Harrison refused to give up. He turned instead to perfecting a watch.

No more worrying about pendulums!* Harrison got straight to work on a ship’s timepiece that uses a metal spring and balance wheel. That good ol’ metal spring and balance wheel would do the trick. No problems with a metal spring and balance wheel, no sir.

Well, maybe one small problem. When metal is warm, it expands slightly. When it cools, it contracts. This spring-powered timepiece was expected to be used in both tropical and arctic conditions. The temperature would change the character of the metal, which would make it less reliable, which would make the timepiece less accurate.

Now what?

* Okay, okay, pendula for you Latin nerds.

Back to the beginning of The Western Civ User’s Guide to Time & Space

Maybe that’s why 18

A reader—who goes by the nomme de keyboard ‘Good Luck’—was intrigued by my question: Why did Magellan take 18 sandglasses on his voyage of circumnavigation? The result was Good Luck found these fascinating articles about Magellan’s voyage and the instruments of navigation/timekeeping available to him. What follows below are his comments and links:

Check out the site below. It indicates there were sandglasses of different time periods and multiple sandglasses might be used to improve accuracy. It also seems possible there were extras in case of breakage.


The article at the link below discusses the use of 14-second and 28-second sandglasses to determine speed. It also describes the use of a 30 minute sandglass used in conjunction with a transverse board to record course and speed. Combined with the 30 minute and 4 hour sandglasses used to measure shifts and watches, as discussed in my previous post, it appears a ship could have had sandglasses of various timespans running at the same time.


The link below provides some information on the inventory Magellan had, part of which is quoted below.

“The fleet that set out employed the best ships and navigation devices of the time: 23 navigation charts, 35 compasses, six pairs of compasses, 21 quadrants, seven astrolabes and 18 sandglasses, among other instruments.”


I can not tell if the inventory listed above was per ship or if it was spread across the five ships that started the voyage. In either case, there appears to be significant redundancy in the compasses, quadrants, and astrolabes, so it seems possible a portion of the 18 sandglasses may have been redundant as well.

So, considering multiple uses, multiple timeframes, likely redundancy, and possibly supporting five ships, having multiple sandglasses makes sense. As to why exactly 18 . . . ?

Thank you, Good Luck! If you change your mind about a drawing just give me a shout.

Back to the beginning of The Western Civ User’s Guide to Time & Space

Let me see what moons are like on Jupiter

The moons of Jupiter travel around her at a regular rate, like the hands of a clock. Galileo thought that you could use the moons as a universal clock. With that clock as a reference point, you could use local time to figure out where you are on Earth.

This sounds like a great idea, but how does it work? I’m guessing that you look at Jupiter, see where her moons are, and calculate where you are on Earth based on which moons you can see. For instance, on Wednesday, May 25, if you’re in North America and you have a telescope you can watch Io and Europa pass in front of Jupiter. If you live on the east coast you’ll see them only starting out; on the west coast you’ll see them only at the end. If you live in the middle of North America you’ll see most of the passage.

Since they know exactly when those moons will be zipping across the face of Jupiter and how long it will take, astronomers are able to make charts of the moons’ progress showing local times everywhere on Earth.

This strikes me as a huge amount of work to figure out where you are on Earth. Then again, I’m holding a cell phone with a GPS (Global Positioning System) so it’s pretty easy for me to know exactly where I am. If I were floating around in the ocean in the 1600s, with no GPS, I imagine I’d be pretty desperate to know exactly where I were and would consider breaking out the old telescope to have a squint at Jupiter and her moons.


Back to the beginning of The Western Civ User’s Guide to Time & Space

Oh, What A Beautiful Ante Meridiem!

The first known use of ‘ante meridiem’ was in 1563. It’s from Latin: ‘meridiem’ means midday or noon. ‘Ante’ means before and ‘post’ means after. So ante meridiem or a.m. is before noon—the hours between midnight and noon. Post meridiem or p.m. is afternoon—the hours between noon and midnight.

A.M. and p.m. are used to describe hours on a 12-hour clock. 10:15 a.m. means 10:15 in the morning; 10:15 p.m. means 10:15 at night. In the military and in Europe, they use a 24-hour clock, so 13:00 means 1:00 p.m.

‘Meridian’ is a different word with 2 meanings. The first meaning is to make an adjective out of meridiem. To say, “She’s wearing an anti-meridian dress” means she’s wearing a dress suitable for the morning. Nobody talks like that nowadays.

Ooooooh—I just gotta paint her in a blaze of yellow and orange!

The second meaning is to describe a line of longitude. The Prime Meridian is Point Zero of east or west. It’s only ad 1563 in this history so we have to wait 200 years before somebody figures out longitude—and where in the world the Prime Meridian is located…

Back to the beginning of The Western Civ User’s Guide to Time & Space


Ante meridiem or antemeridian?

How to slow down a clock

How did they do it?

Those medieval clock-designers came up with a system to slow down the unwinding. First, they attached a gear around the drive-shaft that meshed with a couple of other gears. As you saw with Archimedes’ odometer, the ratio of gear sizes and number of teeth-per-gear can control how fast one gear turns another gear.

That still wasn’t slow enough, though. You want a clock to operate for at least 24 hours before you have to wind it again. How can you make that unwinding even slower?

The answer: an invention called an escapement. An escapement is a mechanical device that interferes with the gear. It actually stops the gear’s movement for a second, then lets go for a second, stops it, lets go, stops it, lets go, stops it, lets go. The first escapement was called the verge and foliot. The verge is a second shaft (not the drive-shaft) with two paddles, or pallets, set at 90 degrees to each other. These pallets interact with a saw-toothed gear which is powered by the drive shaft. As the drive-shaft turns the saw-toothed gear, one pallet stops the gear for a moment until the other pallet is pushed aside.

This stop-and-let-go motion is controlled even further by a bar at the top of the verge shaft, called the foliot. The foliot has a weight hung on each end so that inertia (the weights’ unwillingness to move) slows down oscillation of the verge-shaft. You can control how fast the foliot swings back and forth by moving the weights closer or farther from the center.




Back to the beginning of The Western Civ User’s Guide to Time & Space

Mechanical clocks

Sometime in the 1200s mechanical clocks began being designed and built. When I say mechanical, I mean there are several moving parts in the design. We’ve already seen sundials and water clocks and hourglasses. Water clocks and hourglasses use the release of energy to tell time, as water or sand run out of one container into another. The mechanical clock is different—it uses the release of energy to make it run but has a system of gears and stops to control that energy.

Like those older clocks, medieval mechanical clocks use gravity to supply their energy. A weight is tied to a long rope that is wound around a drive-shaft. When you let go of the weight, the rope unwinds and turns the shaft. The drive-shaft has an arrow attached at its end to point to the hour on a circular clock face. So far, so good—but the drive-shaft will turn really fast for a few seconds, the arrow will whiz around the clock face and then you’d have to wind the rope around again. You still wouldn’t know what time it is. What you need for a clock is a slo-o-o-ow release of energy. How can you slow down the unwinding of that rope?